In conventional toner preparation by extrusion, toner components are mixed in an extruder. The toner material is then extruded through a die, pelletized, subjected to jetting to reduce the size of the particles, and classified. This method forms particles in which the components are evenly dispersed, but requires many separate steps which may take considerable time and involve substantial cost.
Methods of preparing encapsulated toner in situ
are known in the art, such as that process described in U.S. Pat. No. 4,727,011 to Mahabadi et al. Generally, a process of preparing an encapsulated toner in situ comprises the steps of (1) forming a mixture of core monomer, free-radical chemical initiator, pigment and a first shell monomer; (2) forming a stabilized aqueous suspension comprising droplets of the mixture; (3) subjecting this suspension to an interfacial polymerization by the addition of a water-soluble second shell monomer; and (4) initiating a free radical polymerization of the core after the interfacial polymerization is complete by increasing the temperature of the suspension, thus commencing the disassociation of the chemical initiator to free-radicals capable of polymerizing the core monomers, thereby forming encapsulated toner particles.
U.S. Pat. No. 4,307,169 to Matkan discloses electroscopic marking particles comprising microcapsules having a pressure-fixable core and pressure-rupturable shell. The process of preparing these particles involves constant agitation to produce microdroplets of a non-aqueous ink phase encapsulated in a shell which is formed by interfacial polycondensation in an aqueous dispersion of reactants on and about the core. An attritor may be used to produce the ink phase.
In situ methods of preparing non-encapsulated toners are also known. U.S. Pat. No. 4,789,617 to Arahara et al. discloses a process of producing toners comprising the steps of: (1) dispersing a monomer/colorant composition in an aqueous medium at high temperature to form "particles" of the monomer composition; (2) adjusting the aqueous medium to the polymerization temperature; and (3) adding a water-insoluble polymerization initiator to the aqueous medium containing the monomer composition dispersed therein to effect polymerization. According to the examples, an attritor may be used to prepare the monomer composition before addition of the polymerization initiator.
U.S. Pat. No. 4,148,741 to Bayley discloses a method for preparing toners by direct polymerization of polymers. The method comprises the steps of: (1) dispersing in an aqueous medium a monomer having dispersed therein a pigment; (2) agitating the pigmented monomer particles in a reactor to cause a polymerization reaction to form polymerized beads; (3) separating the polymerized beads from the water; and (4) attriting the beads to form toner particles. An initiator or catalyst which is compatible with the monomer may be used in the method.
U.S. Pat. No. 4,293,632 to Dickerson et al. discloses a process for treatment of certain toner materials. An attrition process is used to remove a small portion of a surface of the toner while exposing an underlying inner portion at the same time.
In in situ toner preparation processes, prior to the step of preparing the stabilized aqueous suspension, generally subparticles such as pigment, magnetic material or the like are mixed with the monomer and dispersed therein before droplets of the monomer mixture are formed in an aqueous suspension. However, good dispersion of the subparticles has been a continuing problem, because the subparticles tend to migrate to the monomer-water interface. After the encapsulation process is completed, the subparticles may predominantly be found either at the shell-core interface or even within the shell. Thus, while this process requires fewer steps and thus less time and cost than conventional extrusion methods, there is the inherent problem of forming resin in which the particles are not homogeneously dispersed. Good pigment dispersion is particularly critical in very small toner particles and to provide toner with high projection efficiency in transparencies.
One method of dealing with the problem of providing good pigment dispersion is to use "flushed pigments", wherein a pigment is flushed into a polymeric resin used to prepare the encapsulated toner. Flushed pigments are very expensive, however, and are only available with a limited number of copolymers. The technology for their production is proprietary. Flushed polymers generally contain a high concentration of pigment, and it is generally necessary to "dilute" them with further polymer. However, it is not convenient even in this circumstance to use a different polymer as a "diluent". It is desirable to prepare toners having cores which are not composed of these specific copolymers. Phase separation of the core polymers and flushed pigment is often observed because of the incompatibility of the core polymer and the flushing polymer.
Therefore, polymers which do not require compatibility with specific flushed pigments, which will provide good pigment dispersion and thereby provide the advantages of flushed pigment are desirable.